1. Field of the Invention
The present invention relates to a localized plasmon resonance sensing device and a fiber optic structure; in particular, the present invention relates to a localized plasmon resonance sensing device and a fiber optic structure with an array of sensing regions.
2. Description of Related Art
A fiber optic sensor basically uses an optical fiber to guide light waves generated by a light source to a test area, and variations regarding to certain physical or chemical quantity in the test area, e.g., stress, strain, temperature, refraction index, molecular concentration, may cause changes in the characters of the light wave, therefore through analyses on such changes of light wave characters, it is possible to infer such variations regarding to the physical or chemical quantity. The sensor signal of the fiber optic sensor is barely subject to interferences from electromagnetic noises and magnetic fields when operated in a fiber optic mode, and other hazards in the local environment such as ionizing radiation can be effectively avoided as well; as such, it can be appropriately applied in hostile environments, like within a nuclear power plant. Additionally, one single optical fiber can be simultaneously used as a sensor and a signal transfer line, and the integral size of the fiber optic sensor is usually smaller than that of a conventional sensor together with the transfer line, so it is possible to be deployed in a region spatially tight or extremely challenging for reaching.
The fiber optic sensor employs light as the media for excitation and transmission, rather than usage of electric current or voltage, thus risks in electric shock can be avoided, and it is suitable for medical measurement applications. Fiber optic materials are corrosion-proof, well adapted for deep ocean engineering and applications in a chemically corrosive environment, and provide good biocompatibility as well. The glass optical fiber demonstrates better temperature tolerance than the metal strain gauge, whose long-term stability and fatigue lifecycle are both higher than the resistive stain gauge, accordingly fitting for surveillances in long duration of time. Since the optical fiber is originally applied in the field of long distance communication, relevant technologies in fiber optic sensor can be conveniently exploited from technologies in long distance telemetry. Furthermore, wavelength division multiplexing technology developed in optical communication also facilitates multi-point telemetry with one single optical fiber, so the fiber optic sensor now has been comprehensively used in various fields such as aviation, medication, chemistry, geotechnical engineering, civil engineering and so forth.
Please refer first to FIG. 1, wherein a diagram illustrating the basic structure of an optical fiber is shown. The optical fiber in essence is an optical waveguide of an axially symmetric cylindrical structure, and, radially from the axle to the outside, can be divided into three layers, respectively the core 11, the cladding 12 and the jacket 13. The core 11 and the cladding 12 are basic elements for light transfer in the optical fiber and core 11 has a higher refractive index than that of cladding 12. The jacket 13 acts as the protection layer against external environment.
The well-known principle of the fiber optic sensor is, for example, to measure a certain physical (chemical) quantity, it first relates one characteristic of light to the variation of such a physical (chemical) quantity, next performs measurements on the result caused by such a variation, then the magnitude of the physical (chemical) quantity to be measured can be indirectly inferred. Regarding to an example of measurement on a physical quantity, if it is now to measure the torsion of a piece of mechanical part, bending the optical fiber leads to escape of light energy from the core and energy loss, and higher torsion results in more significant light energy loss; in other words, light energy is subject to the variation of torsion. Accordingly, by placing the optical fiber optic onto the mechanical part, it is possible to measure the intensity of transmitted light through the optical fiber, indirectly inferring the torsion of the mechanical part sensed by the optical fiber; on the other hand, for an example of chemical value measurement, a gas can absorb light of a certain specific wavelength and the absorption is proportional to the concentration of the gas. Therefore, an appropriate light is guided by the optical fiber to the test area so as to allow part of the light to interact with the gas in the test area, and get analyzed at the other end of the optical fiber by the spectrum thereof for measurement of intensity attenuation at the particular light wavelength such that it is possible to infer the concentration of the gas. Herein the modulation of light characteristic accountable for the variation of the physical (chemical) quantity may occur inside the optical fiber optic or at the exterior of the optical fiber as well; modulation of different characteristics of light may be measured individually or interactively, wherein the modulation mechanism may comprise:
1. absorption modulation;
2. chromatic dispersion modulation;
3. scattering based modulation;
4. luminescence-fluorescence based modulation;
5. refractive index based modulation;
6. geometric effect based modulation;
7. interferometric and phase modulation;
8. wavelength modulation; and
9. Doppler's effect modulation.
In addition, according the location where the sensing modulation occurs, different modulation mechanisms can be categorized as three major types: (1) extrinsic type, (2) intrinsic type, and (3) evanescent type characterized between the aforementioned two types. For the extrinsic typed sensor, it means that light, after guided to the test area through the optical fiber, momentarily leaves the optical fiber and is modulated by the external environment, then coupled into the original optical fiber or another optical fiber, and transferred to a signal generator for signal interpretation, wherein the optical fiber acts simply as a signal transmission line without participating in sensing operations; in the intrinsic typed sensor, on the other hand, light wave basically remains in the optical fiber all the time, and modulation from external environment cause changes in the internal characteristics of the optical fiber, thereby affecting a certain feature of the light wave (e.g., wavelength); the evanescent sensor uses changes of light energy loss in the evanescent field of the optical fiber caused by modulation from external environment to determine the environmental parameter to be detected; although such type of sensor may similarly involve in part of the light energy leaving the fiber core like the extrinsic typed sensor, a difference exists in that the modulation mechanism acts inside the cladding of the optical fiber, and the optical fiber is not only used as a signal transmission line but a sensing component as well.
To meet the requirements on sensing operations, the desktop Fiber Optic-Localized Plasmon Resonance (FO-LPR) sensing platform and implanted FO-LPR sensing system are developed. The implanted FO-LPR sensing system can be used to directly measure variations of specific biological molecules inside a living body, then the optical fiber of a suitable size can be selected based on the size of the object (e.g., organ or tissue) subject to the implantation. For example, if the optical fiber having a core of larger size is applied to a small animal, or to some small organs or tissues in a human body, such a larger size fiber may undesirably cause damages to a certain extent to the living body itself during implantation; serious damage may jeopardize its life while minor damage can result in additional metabolites or inflammation reactions in the living body, thus interfering the results originally intended to be measured.